1. Field of the Invention
The present invention relates to an inspection apparatus for inspecting electric and luminous characteristics of semiconductor light emitting elements such as a light emitting diode (LED), a laser diode and the like, and more specifically relates to an estimation apparatus for a semiconductor light emitting element capable of inspecting the light emitting element as a wafer before attaching electrodes and the like.
2. Discussion of the Background
While manufacturing a semiconductor device by using a semiconductor wafer, it is necessary to select wafers by previously investigating the characteristics of the wafers. Unless the determination is properly done as to whether wafers have defects or not, yield and reliability decrease to result in an increase in manufacturing cost. In the same manner, it is necessary to judge the quality of elements and to properly select the elements on the basis of a characteristic value which is investigated from each of the elements after a plurality of elements are formed on the semiconductor wafer. Especially, since the application of a LED recently extends to not only a single lamp but also to an array and a display panel, the LED pellets having higher quality are required in large quantities.
In a conventional epitaxial wafer for the LED, after the wafer on which elements are previously formed is divided into a plurality of pellets, electric and luminous characteristics are investigated by a sampling inspection. Particularly, it is widely performed that a pellet is selected in accordance with the luminous efficiency.
However, it is difficult for the conventional method to combine shortening a time spent on a work and an improvement of an inspection accuracy. Namely, since a sampling number is limited from the viewpoint of shortening a time, an inspection accuracy decreases, thereby resulting in that evenness between the selected pellets can not be obtained in a good reproduction. In the case of the light emitting diode, a discrepancy of characteristics in a wafer surface and between wafers becomes large at each lot, and the reappearance is insufficient. As a result, there is a luminance discrepancy in a screen of the completed display. On the contrary, since the sampling number should increase for improving an accuracy, an inspection time becomes longer.
Therefore, there is provided a selection method at a wafer stage before dividing the water into a plurality of pellets. This method is a practical application of a die sort method which is used for manufacturing an integrated circuit (IC). When the die sort method applies to an LED, an electric division between elements is not performed at the wafer stage in the LED, and for example, after electrodes of each of the elements are formed, the elements are divided by performing a half die in which the wafer is attached to an adhesive sheet and a groove is cut on the wafer. Each of the elements is sequentially scanned to drive a light emission, and a luminous efficiency is measured on the basis of a light detection level. However, scattering between adjacent pellets can not be avoided even though the elements are divided, thereby resulting in a problem that a correct measured value can not be obtained. As a result of an actual attempt, it is impossible to obtain an accuracy sufficient to the extent capable of withstanding a practical use because there many discrepancies against a measured value after dividing the wafer into a plurality of pellets. Furthermore, since a scar of a probe remains by any methods, it is easy for an unevenness of a bonding strength in the latter bonding step to result.